A flexible direct current transmission system and its direct current fault handling method

Abstract

The invention discloses a flexible direct current transmission system and a direct current fault processing method thereof. The system comprises ABC three-phase converter valves, wherein the converter valve of each phase is divided into an upper bridge arm and a lower bridge arm, and the upper bridge arm and the lower bridge arm are both respectively cascaded by a plurality of sub-modules; one side of a power transmission system formed by the ABC three-phase converter valves is connected to an alternating current network, and the other side of the power transmission system is connected to a direct current overhead line; a bleeder resistor R is connected between the power transmission system and the DC overhead line; through adding the bleeder resistor R and controlling the bleeder resistor to put into the system before a direct current breaker is opened, after the direct current breaker is opened, the resistance lasts for some time, and after the fault current is reduced to be lower than an overcurrent threshold value, the direct current bleeder resistor R is disconnected; the method provides an access to a circuit, and the current cannot flow into a capacitor through a diode. The system is simple in structure and the method is simple and effective, and a problem that a direct current fault processing process is easy to cause overvoltage of the capacitor voltage and diode overcurrent can be solved.

Description

technical field [0001] The invention belongs to the technical field of flexible power transmission and distribution, and relates to a DC fault processing method of a flexible DC power transmission system. Background technique [0002] Modular Multilevel Converter (MMC) for flexible DC transmission can use sub-modules (Sub Modules, SM) of different topologies, such as half-bridge modules, full-bridge modules and twin sub-modules. [0003] When a DC ground fault occurs, the flexible DC transmission system composed of the full-bridge module and the twin sub-modules can connect the module capacitors into the fault loop to provide a reverse voltage by means of device blocking, thereby suppressing the fault current. The half-bridge module does not have the above functions, so when the DC ground fault occurs in the half-bridge module, a relatively large fault current will flow through the device. At present, the commonly used method is to disconnect the AC switch to block the DC cu...

AI Technical Summary

Problems solved by technology

[0010] The purpose of the present invention is to provide a flexible direct current transmission system and its direct current fault processing method, so as to overcome the problems in the prior art that dealing with direct current faults easily lead to capacitor voltage overvoltage and diode overcurrent

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